Infrared spectrum of the water–carbon monoxide complex in the CO stretching region

Abstract

The CO-stretching vibration–rotation spectra of water–carbon monoxide complexes (H2O–CO, D2O–CO, and HDO–CO) in the 2150 cm−1 region have been studied in a supersonic slit jet expansion using a rapid-scan tunable diode laser spectrometer. Accurate band origins and rotational parameters were determined in order to characterize the CO stretching dependence of the bonding in this system. The symmetric isotopes, H2O–CO and D2O–CO, exhibited two distinct nuclear spin components arising from proton- (deuteron-) exchange tunneling, as observed previously in the microwave spectrum. The tunneling splittings were found to increase by about 10% upon excitation of the CO stretching vibration, indicating a lowering of the tunneling barrier in the excited state. The D-bonded isomer, HOD–CO, of the unsymmetrical isotope was observed prominently, and the higher-energy H-bonded isomer, DOH–CO, was also detected for the first time. From the intensities of their spectra, the energy difference between these two forms of the complex was estimated to be 12.4±2.5 cm−1.